CDMA wireless communication systems allow multiple remote terminals to use multiple code channels modulated upon a common carrier frequency to communicate with a base station. CDMA systems have several advantages over alternative wireless approaches such as time division multiple access (TDMA) or frequency division multiple access (FDMA). CDMA system channel capacity can be higher and there is an improvement in multipath fading. However, systems which use frequency division duplex (FDD) to provide for 2 way wireless communication suffer from differing multipath environments on uplink and downlink communication frequencies. Smart antenna systems can improve communication between a base station and a remote terminal by providing additional robustness to CDMA "coding gain". The additional robustness is provided by directing each downlink signal toward corresponding remote terminal thereby reducing interfering signals received at one remote terminal intended for another remote terminal. The different multipath environments of the uplink and downlink deter optimization of a smart antenna based communication system. Thus, what is needed is a smart antenna CDMA communication system which provides for a common frequency for both uplink and downlink communications. Also what is needed is a communication system which enables improved spacial estimations of a remote terminal in order to improve the directional characteristics of a smart antenna.
Synchronous CDMA systems provide improved coding gain over asynchronous CDMA systems. However, synchronization signals can use significant bandwidth or require complex processing in the base station or remote terminal, thereby increasing the cost of the communication system. Thus, what is needed is a communication system which provides synchronous CDMA communication on both the uplink and downlink communication channels without adding significant cost or bandwidth to the communication system.
In a typical communication system, base station signals may be received by numerous remote terminals, while only a few remote terminals are communicating information with the base station. However, when a call is initiated, it is desirable that the link between the remote terminal and the base station be established as quickly as possible. Therefore what is needed is a CDMA communication system which provides for rapid establishment of a communication link between a remote terminal and a base station. Two remote terminals attempting to simultaneously establish a link may cause collision interference at the base station, therefore what is needed is a communication system which efficiently addresses recovery from such collisions. Furthermore, during the establishment of the communication link, large course adjustment in synchronization and power levels of the remote terminal should be provided. However, once the link is established smaller fine adjustments of synchronization and power control if used, would reduce overhead. However, the large course adjustment signals use more channel capacity than needed once a link is established and consequently waste channel capacity. Thus, what is needed is a communication system which reduces the channel capacity used to synchronize a remote terminal once a link is established.